EP0642427A1 - Method of detecting a deflated tyre on a vehicle. - Google Patents

Method of detecting a deflated tyre on a vehicle.

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Publication number
EP0642427A1
EP0642427A1 EP94910552A EP94910552A EP0642427A1 EP 0642427 A1 EP0642427 A1 EP 0642427A1 EP 94910552 A EP94910552 A EP 94910552A EP 94910552 A EP94910552 A EP 94910552A EP 0642427 A1 EP0642427 A1 EP 0642427A1
Authority
EP
European Patent Office
Prior art keywords
factor
vehicle
detecting
deciding
deflated
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP94910552A
Other languages
German (de)
French (fr)
Other versions
EP0642427B1 (en
Inventor
David Jones
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Sumitomo Rubber Industries Ltd
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Sumitomo Rubber Industries Ltd
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Filing date
Publication date
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Publication of EP0642427A1 publication Critical patent/EP0642427A1/en
Application granted granted Critical
Publication of EP0642427B1 publication Critical patent/EP0642427B1/en
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Expired - Lifetime legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
    • B60C23/00—Devices for measuring, signalling, controlling, or distributing tyre pressure or temperature, specially adapted for mounting on vehicles; Arrangement of tyre inflating devices on vehicles, e.g. of pumps or of tanks; Tyre cooling arrangements
    • B60C23/06—Signalling devices actuated by deformation of the tyre, e.g. tyre mounted deformation sensors or indirect determination of tyre deformation based on wheel speed, wheel-centre to ground distance or inclination of wheel axle
    • B60C23/061—Signalling devices actuated by deformation of the tyre, e.g. tyre mounted deformation sensors or indirect determination of tyre deformation based on wheel speed, wheel-centre to ground distance or inclination of wheel axle by monitoring wheel speed
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
    • B60C23/00—Devices for measuring, signalling, controlling, or distributing tyre pressure or temperature, specially adapted for mounting on vehicles; Arrangement of tyre inflating devices on vehicles, e.g. of pumps or of tanks; Tyre cooling arrangements
    • B60C23/06—Signalling devices actuated by deformation of the tyre, e.g. tyre mounted deformation sensors or indirect determination of tyre deformation based on wheel speed, wheel-centre to ground distance or inclination of wheel axle

Definitions

  • This invention relates to a method of detecting a deflated tyre on a vehicle suitable for cars, trucks or the like.
  • Prior applications such as French Patent Publication No. 2568519 and European Patent Publication No. 291 217 propose using wheel speed signals from the vehicle wheels such as for example the signals from an anti-lock braking system which are multi-pulse signals of typically 48 to 96 pulses per revolution of each wheel.
  • the prior art system compares the speed derived signals in various ways, and also attempt to overcome errors due to vehicle factors such as cornering, braking, accelerating, uneven or changing loads, which can cause changes in the speed signals which are larger than those caused by a tyre deflation of for example 0.4 bar.
  • French Patent Publication No. 2568519 avoided errors of this type by monitoring the speeds of the diagonally opposed pairs of wheels for a long time or distance period so that it averaged out effectively cornering of the vehicle. The result however was that the device operated very slowly taking many Kilometres to sense a pressure loss.
  • European Patent Publication No. 291 217 improved the situation by calculating the lateral and longitudinal acceleration of the vehicle using the same four wheel speed signals and setting fixed limits above which the detection system was inhibited to avoid false signals due to cornering and acceleration. This inhibition of detection however meant that for a proportion of the time of vehicle running the system was not sensing punctures, the actual proportion depending upon the type of roads and the way the vehicle was being driven.
  • each vehicle has different characteristics due to the position of the centre of gravity and the type of suspension and these different characteristics when cornering produce additional deflections in the outer pairs of tyres with regard to the inner pairs of tyres.
  • a method of detecting a deflated tyre on a vehicle by comparing the rolling radii of the tyres by means of comparing angular velocity speed signals from wheel speed sensors one at each wheel characterised by calculating an error value DEL'
  • DELCOR (A x LAT) + (B x LAT 2 ) wherein A and B are vehicle related constants, and operating a tyre warning indicator provided in the vehicle to indicate that at least one tyre is deflated when it is sensed that the magnitude of the corrected error value DEL is in the range 0.05 to 0.5.
  • the tyre warning indicator is operated when the magnitude of the corrected error value is in the range 0.1 to 0.3.
  • the vehicle related constants A and B may have values in the range -5.0E-7 to +5.0E-7 and -4.0E-9 to +4.0E-9 respectively.
  • the correction factor LAT is found by calculating from the four angular velocity values Cl, C2,
  • MC4 C4/[ [ (C2 + C4)/(C1 + C3)] x [ (C3 + C4)/(C1 + C2)]] summing the four deciding factors and multiplying this sum by a centralising constant (K) to give a central deciding factor (MPSD) and selecting the correction factor (LAT) as follows, if the first or second deciding factor (MCI or
  • LAT (Cl + C3 - C2 - C4) x (Cl + C2 + C3 + C4).
  • the centralising constant used in the derivation of the central deciding factor MPSD may be in the range of 0.250125 to 0.250625 and preferably has a value of
  • the particular tyre which is deflated may be detected by calculating for each wheel a deflation indicating factor IMC1, IMC2, IMC3 and IMC4 respectively and then selecting the factor having the largest numerical value, the deflation indicating factors being calculated as follows:
  • IMC1 Cl if the first deciding factor (MCI) is greater than the central deciding factor (MPSD) then
  • IMC2 C2/[ ((C4 C3)/2) + 0.5]
  • IMC3 C3/[ ((C4/C2)/2) + 0.5]
  • IMC4 C4 [[ ((C4/C3)/2) + 0.5] x [ ((C4/C2)/2) + 0.5]]; if the second deciding factor (MC2) is greater than the central deciding factor (MPSD) then
  • IMC2 C2/[ ((C4/C3)/2) + 0.5]
  • IMC3 C3/[ ((C3/Cl)/2) + 0.5]
  • IMC4 C4/[ [ ((C4/C3)/2) + 0.5] x [ ((C3/Cl)/2) + 0.5]]; if the third deciding factor (MC3) is greater than the central deciding factor (MPSD) then
  • IMC2 C2/[ ((C2/Cl)/2) + 0.5]
  • IMC3 C3/[ ((C4/C2)/2) + 0.5]
  • IMC4 C4/[ [ ((C2/Cl)/2) + 0.5] x [ ((C4/C2)/2) + 0.5]]; if the fourth deciding factor (MC4) is greater than the central deciding factor (MPSD) then
  • IMC2 C2/[ ((C2/Cl)/2) + 0.5]
  • IMC3 C3/[ ((C3/Cl)/2) + 0.5]
  • IMC4 C4/[[ ((C2/Cl)/2) + 0.5] x [ ((C3/Cl)/2) + 0.5]]; or if none of the deciding factors (MCI, MC2, MC3, MC4) is greater than the central deciding (MPSD) factor then
  • IMC2 C2/[ (((C2 + C4)/(C1 + C3))/2) + 0.5]
  • IMC3 C3/[ (((C3 + C4)/(C1 + C2))/2) + 0.5]
  • IMC4 C4/[ [ (((C3 + C4)/(C1 + C2))/2) + 0.5] x [ (((C2 + C4)/(C1 + C3))/2) + 0.5]].
  • an initialisation procedure may be carried out. This monitors the signals under normal driving conditions and enables constants for each wheel to be determined to allow for variations.
  • Figure 1 is a schematic diagram showing a deflation warning device for a car having four wheels
  • Figure 2 is a schematic diagram showing the sequence of computations used to determine if a deflated tyre exists and decide which one is deflated;
  • Figure 3 is a schematic diagram showing the sequence of computations used in determining the correction factor LAT.
  • the apparatus shown in Figure 1 provides a deflation warning device for a vehicle having four wheels 1, 2, 3 and 4. Wheels 1 and 2 are the left- and right- hand front wheels respectively and wheels 3 and 4 are the left- and right-hand rear wheels respectively. Each wheel has a toothed wheel device associated with it of the type designed and fitted to provide a digital signal comprising a magnetic pick-up of the type used for a vehicle anti ⁇ skid system of the electronic type-often commonly known as ABS braking system. Each pick-up is additionally connected in this case to a deflation warning detection system which uses the same digital signal as the ABS system.
  • the electronic signals from each of the four wheels are carried through cables 5 to four separate inputs 6, 7, 8 and 9 of a central processing unit 10.
  • Four separate indicator lights 12, 13 14 and 15 are provided one for each wheel 1, 2, 3 and 4. Thiese indicator lights may be most conveniently mounted on the vehicle dashboard.
  • the central processing unit 10 is basically a microprocessor which monitors the four signals and compares them to determine if an outward signal is to be sent to operate an indicator light to warn of a deflated tyre.
  • the microprocessor 10 may be the same microprocessor as the ABS system. Alternatively a separate microprocessor may be provided.
  • the respective values of the total digital pulse signals from each of the wheels 1, 2, 3 and 4 in a five second period are Cl, C2, C3 and C4 respectively.
  • the central processing unit 10 computes these frequency values as will be described below to determine whether or not to send a deflation warning signal to one of the warning lights 12, 13, 14 or 15.
  • the first operation in the method of the invention is to calculate from the actual wheel speed values C1-C4 an error value DEL' where
  • a correction factor LAT is calculated according to the magnitude of respective deciding factors MC1-MC2 for each wheel in comparison to a central deciding factor MPSD.
  • the central deciding factor is equal to the sum for the four deciding factors MC1-MC2 multiplied by a centralising constant K which in this embodiment is selected to be 0.25025.
  • corrected error factor DEL error factor DEL' - DELCOR
  • DELCOR (LAT x A) + (LAT 2 x B)
  • a and B are vehicle related constants which allow for vehicle factors such as the track and other dimensions of the vehicle and characteristics of the suspension particularly in relation to side-to-side tilt.
  • a and B are vehicle related constants which allow for vehicle factors such as the track and other dimensions of the vehicle and characteristics of the suspension particularly in relation to side-to-side tilt.
  • the values of these constants A and B for a particular vehicle may be determined by experiment. Values of the constants which have been established for various cars are shown below in Table 1.
  • the central processing unit 10 decides if the value of DEL is in the range of 0.05 to 0.5 which indicates the presence of a deflates tyre.
  • Values of DEL below 0.05 are the result of minor statistical variation in the counts from each wheel whereas values of DEL greater than 0.5 indicate a relatively uncommon occurrence such as wheel spin or a locked wheel and are greater than the effect of a punctured tyre.
  • the central processing unit 10 finds that the corrected error value is between 0.05 and 0.5 then the method of the invention moves on to the next stage which is to determine which tyre is deflated. Otherwise the system continues to monitor wheel speeds.
  • IMC2 C2/[ ((C4/C3)/2) + 0.5]
  • IMC3 C3/[ ((C4/C2)/2) + 0.5]
  • IMC4 C4/[ [ ((C4/C3)/2) + 0.5] x [ ((C4/C2)/2) + 0.5]]; if the second deciding factor (MC2) is greater than the central deciding factor (MPSD) then
  • IMC2 C2/[ ((C4/C3)/2) + 0.5]
  • IMC3 C3/[ ((C3/Cl)/2) + 0.5]
  • IMC4 C4/[ [ ((C4/C3)/2) + 0.5] x [ ((C3/Cl)/2 + 0.5)]]; if the third deciding factor (MC3) is greater than the central deciding factor (MPSD) then
  • IMC2 C2/[ ((C2/Cl)/2) + 0.5]
  • IMC3 C3/[ ((C4/C2)/2) + 0.5]
  • the central processing unit compares these to determine which wheel has the factor of the largest magnitude.
  • a signal is then sent to operate the indicator light corresponding to that wheel in order to alert the driver that the tyre concerned has deflated.
  • the warning signal is only sent after three sets of deflation indicating factors, calculated from successive sets of wheel speed data, all indicate that a particular tyre is deflated. Whilst the above embodiment has illustrated the method of the invention using the signal data from a multi-toothed wheel system typically producing 48 or 96 pulses per wheel revolution the invention can equally be used with other wheel speed sending systems.
  • the method may be used with a simple system which uses a single pulse per revolution to compute the time period for one rotation of each wheel, in which case it will be necessary to multiply the wheel speeds by a constant factor to obtain data in the necessary form.
  • Values of A and B in the ranges -2.0E-7 to +2.0E-7 and -2.0E-9 to +1.0E-9 have been found particularly useful in practise of the invention.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Measuring Fluid Pressure (AREA)
  • Tires In General (AREA)
  • Testing Of Balance (AREA)

Abstract

PCT No. PCT/JP94/00501 Sec. 371 Date Nov. 16, 1994 Sec. 102(e) Date Nov. 16, 1994 PCT Filed Mar. 29, 1994 PCT Pub. No. WO94/22681 PCT Pub. Date Oct. 13, 1994A method and device for detecting a deflated tire on a vehicle by comparing the rolling radii of the tires by means of comparing angular velocity speed signals from wheel speed sensors, one at each wheel, characterized by calculating an error value DEL', where <IMAGE> wherein C1, C2, C3 and C4 are angular velocity values for left-hand front, right=hand front, left-hand rear and right-hand rear wheels of the vehicle respectively, determining a correction factor LAT, calculating a corrected error value DEL where DEL=DEL'-DELCOR wherein DELCOR=(LATxA)+(BxLAT2) wherein A and B are vehicle related constants, and operating a tire warning indicator provided in the vehicle to indicate that at least one tire is deflated when it is sensed that the magnitude of the corrected error value DEL is in the range 0.05 to 0.5.

Description

DESCRIPTION
METHOD OF DETECTING A DEFLATED TYRE ON A VEHICLE
TECHNICAL FIELD
This invention relates to a method of detecting a deflated tyre on a vehicle suitable for cars, trucks or the like.
BACKGROUND ART
Prior applications such as French Patent Publication No. 2568519 and European Patent Publication No. 291 217 propose using wheel speed signals from the vehicle wheels such as for example the signals from an anti-lock braking system which are multi-pulse signals of typically 48 to 96 pulses per revolution of each wheel. The prior art system compares the speed derived signals in various ways, and also attempt to overcome errors due to vehicle factors such as cornering, braking, accelerating, uneven or changing loads, which can cause changes in the speed signals which are larger than those caused by a tyre deflation of for example 0.4 bar.
French Patent Publication No. 2568519 avoided errors of this type by monitoring the speeds of the diagonally opposed pairs of wheels for a long time or distance period so that it averaged out effectively cornering of the vehicle. The result however was that the device operated very slowly taking many Kilometres to sense a pressure loss. European Patent Publication No. 291 217 improved the situation by calculating the lateral and longitudinal acceleration of the vehicle using the same four wheel speed signals and setting fixed limits above which the detection system was inhibited to avoid false signals due to cornering and acceleration. This inhibition of detection however meant that for a proportion of the time of vehicle running the system was not sensing punctures, the actual proportion depending upon the type of roads and the way the vehicle was being driven.
The real difficulty with these types of systems is that, apart from the lateral acceleration of the vehicle which occurs during cornering causing increased deflection of the outer pair of wheels compared to the inner pair of wheels, each vehicle has different characteristics due to the position of the centre of gravity and the type of suspension and these different characteristics when cornering produce additional deflections in the outer pairs of tyres with regard to the inner pairs of tyres.
However the vehicle characteristics make the tyre deflections different in each of the tyres. Similar problems occur due to vehicle characteristics in the deflections in the front pair of tyres compared to the rear pair when the vehicle brakes, and vice- versa when the vehicle accelerates.
It is an object of the present invention to provide a method of detecting a deflated tyre on a vehicle which accommodates the above changes, avoiding false signals and detecting deflation for substantially all the time when the vehicle is running.
DISCLOSURE OF INVENTION According to one aspect of the present invention there is provided a method of detecting a deflated tyre on a vehicle by comparing the rolling radii of the tyres by means of comparing angular velocity speed signals from wheel speed sensors one at each wheel characterised by calculating an error value DEL' where
__ , _ [ (Cl+C4)/2-(C2+C3)/2] x 100
(Cl + C2 + C3 + C4)/4
where Cl, C2, C3 and C4 are angular velocity values for left-hand front, right-hand front, left-hand rear and right-hand rear wheels of the vehicle respectively, determining a correction factor LAT, calculating a corrected error value DEL where DEL = DEL' - DELCOR wherein
DELCOR = (A x LAT) + (B x LAT2) wherein A and B are vehicle related constants, and operating a tyre warning indicator provided in the vehicle to indicate that at least one tyre is deflated when it is sensed that the magnitude of the corrected error value DEL is in the range 0.05 to 0.5. Preferably the tyre warning indicator is operated when the magnitude of the corrected error value is in the range 0.1 to 0.3.
The vehicle related constants A and B may have values in the range -5.0E-7 to +5.0E-7 and -4.0E-9 to +4.0E-9 respectively.
The correction factor LAT is found by calculating from the four angular velocity values Cl, C2,
C3 and C4 respective first, second, third and fourth deciding factors (MCI, MC2, MC3, MC4) where MCI = Cl
MC2 = C2/[ (C2 + C4)/(C1 + C3)]
MC3 = C3/[ (C3 + C4)/(C1 + C2)]
MC4 = C4/[ [ (C2 + C4)/(C1 + C3)] x [ (C3 + C4)/(C1 + C2)]] summing the four deciding factors and multiplying this sum by a centralising constant (K) to give a central deciding factor (MPSD) and selecting the correction factor (LAT) as follows, if the first or second deciding factor (MCI or
MC2) is greater than the central deciding factor (MPSD) then LAT = 2 x (C3 - C4) x (Cl + C2 + C3 + C4), if the third or fourth deciding factor (MC3 or MC4) is greater than the central deciding factor (MPSD) then
LAT = 2 x (Cl - C2) x (Cl + C2 + C3 + C4), or if none of the deciding factors (MCI, MC2, MC3 or MC4) is greater than the central deciding factor (MPSD) then
LAT = (Cl + C3 - C2 - C4) x (Cl + C2 + C3 + C4).
The centralising constant used in the derivation of the central deciding factor MPSD may be in the range of 0.250125 to 0.250625 and preferably has a value of
0.25025.
The particular tyre which is deflated may be detected by calculating for each wheel a deflation indicating factor IMC1, IMC2, IMC3 and IMC4 respectively and then selecting the factor having the largest numerical value, the deflation indicating factors being calculated as follows:
IMC1 = Cl if the first deciding factor (MCI) is greater than the central deciding factor (MPSD) then
IMC2 = C2/[ ((C4 C3)/2) + 0.5]
IMC3 = C3/[ ((C4/C2)/2) + 0.5]
IMC4 = C4 [[ ((C4/C3)/2) + 0.5] x [ ((C4/C2)/2) + 0.5]]; if the second deciding factor (MC2) is greater than the central deciding factor (MPSD) then
IMC2 = C2/[ ((C4/C3)/2) + 0.5]
IMC3 = C3/[ ((C3/Cl)/2) + 0.5]
IMC4 = C4/[ [ ((C4/C3)/2) + 0.5] x [ ((C3/Cl)/2) + 0.5]]; if the third deciding factor (MC3) is greater than the central deciding factor (MPSD) then
IMC2 = C2/[ ((C2/Cl)/2) + 0.5]
IMC3 = C3/[ ((C4/C2)/2) + 0.5]
IMC4 = C4/[ [ ((C2/Cl)/2) + 0.5] x [ ((C4/C2)/2) + 0.5]]; if the fourth deciding factor (MC4) is greater than the central deciding factor (MPSD) then
IMC2 = C2/[ ((C2/Cl)/2) + 0.5]
IMC3 = C3/[ ((C3/Cl)/2) + 0.5]
IMC4 = C4/[[ ((C2/Cl)/2) + 0.5] x [ ((C3/Cl)/2) + 0.5]]; or if none of the deciding factors (MCI, MC2, MC3, MC4) is greater than the central deciding (MPSD) factor then
IMC2 = C2/[ (((C2 + C4)/(C1 + C3))/2) + 0.5]
IMC3 = C3/[ (((C3 + C4)/(C1 + C2))/2) + 0.5]
IMC4 = C4/[ [ (((C3 + C4)/(C1 + C2))/2) + 0.5] x [ (((C2 + C4)/(C1 + C3))/2) + 0.5]].
Whilst the invention in fact compares the angular velocities of the wheels it should be understood that this can be done by comparing the times for one full turn of each wheel or by comparing digital signals for multipulse wheel speed generators.
To allow for tyres from different manufacturers which may therefore be of different sizes an initialisation procedure may be carried out. This monitors the signals under normal driving conditions and enables constants for each wheel to be determined to allow for variations.
BRIEF DESCRIPTION OF DRAWINGS
Figure 1 is a schematic diagram showing a deflation warning device for a car having four wheels;
Figure 2 is a schematic diagram showing the sequence of computations used to determine if a deflated tyre exists and decide which one is deflated; and
Figure 3 is a schematic diagram showing the sequence of computations used in determining the correction factor LAT.
BEST MODE FOR CARRYING OUT THE INVENTION
Further aspects of the present invention will become apparent from the following description, by way of example only, of one embodiment in conjunction with the attached diagrammatic drawings. The apparatus shown in Figure 1 provides a deflation warning device for a vehicle having four wheels 1, 2, 3 and 4. Wheels 1 and 2 are the left- and right- hand front wheels respectively and wheels 3 and 4 are the left- and right-hand rear wheels respectively. Each wheel has a toothed wheel device associated with it of the type designed and fitted to provide a digital signal comprising a magnetic pick-up of the type used for a vehicle anti¬ skid system of the electronic type-often commonly known as ABS braking system. Each pick-up is additionally connected in this case to a deflation warning detection system which uses the same digital signal as the ABS system.
The electronic signals from each of the four wheels are carried through cables 5 to four separate inputs 6, 7, 8 and 9 of a central processing unit 10. Four separate indicator lights 12, 13 14 and 15 are provided one for each wheel 1, 2, 3 and 4. Thiese indicator lights may be most conveniently mounted on the vehicle dashboard.
The central processing unit 10 is basically a microprocessor which monitors the four signals and compares them to determine if an outward signal is to be sent to operate an indicator light to warn of a deflated tyre. In the case where the vehicle already has an ABS system fitted then the microprocessor 10 may be the same microprocessor as the ABS system. Alternatively a separate microprocessor may be provided. The respective values of the total digital pulse signals from each of the wheels 1, 2, 3 and 4 in a five second period are Cl, C2, C3 and C4 respectively. The central processing unit 10 computes these frequency values as will be described below to determine whether or not to send a deflation warning signal to one of the warning lights 12, 13, 14 or 15.
The sequence of operations used in this computation is shown schematically in Figure 2.
The first operation in the method of the invention is to calculate from the actual wheel speed values C1-C4 an error value DEL' where
___ , _ [ (Cl+C4)/2-(C2+C3)/2] x 100 DEL — •
(Cl + C2 + C3 + C4)/4
However because the actual wheel speed values may be distorted due to vehicle factors such as cornering, braking, accelerating or uneven loads which give rise to a greater effect than that caused by a tyre deflation it is necessary to correct this calculated error value to remove these vehicle effects.
To correct the error value DEL' a correction factor LAT is calculated according to the magnitude of respective deciding factors MC1-MC2 for each wheel in comparison to a central deciding factor MPSD. The central deciding factor is equal to the sum for the four deciding factors MC1-MC2 multiplied by a centralising constant K which in this embodiment is selected to be 0.25025. The value of the correction factor LAT is then calculated depending on which if any of the four deciding factors MC1-MC4 is greater in magnitude than the central deciding factor MPSD as follows: if MCI or MC2 > MPSD then LAT = 2 x (C3 - C4) x (Cl + C2 + C3 + C4) or if MC3 or MC4 > MPSD then LAT = 2 x (Cl - C2) x (Cl + C2 + C3 + C4) otherwise
LAT = (Cl + C3 - C2 - C4) x (Cl + C2 + C3 + C4) This sequence of operations is shown in Figure
The calculated error value DEL' is then corrected to remove vehicle effects to give a corrected error value DEL according to the following equation corrected error factor DEL = error factor DEL' - DELCOR wherein DELCOR = (LAT x A) + (LAT2 x B) wherein A and B are vehicle related constants which allow for vehicle factors such as the track and other dimensions of the vehicle and characteristics of the suspension particularly in relation to side-to-side tilt. The values of these constants A and B for a particular vehicle may be determined by experiment. Values of the constants which have been established for various cars are shown below in Table 1.
TABLE 1
Vehicle Year Constant A Constant B
Audi 100 1992 -1.8E-07 -6.2E-10
BMW 850i 1992 +1.0E-07 +4.6E-10
Peugeot 405 1992 -3.3E-08 -1.8E-10
Rover 820SLi 1992 +1.4E-07 -1.4E-09 Having calculated the corrected error value DEL the central processing unit 10 then decides if the value of DEL is in the range of 0.05 to 0.5 which indicates the presence of a deflates tyre. Values of DEL below 0.05 are the result of minor statistical variation in the counts from each wheel whereas values of DEL greater than 0.5 indicate a relatively uncommon occurrence such as wheel spin or a locked wheel and are greater than the effect of a punctured tyre.
If the central processing unit 10 finds that the corrected error value is between 0.05 and 0.5 then the method of the invention moves on to the next stage which is to determine which tyre is deflated. Otherwise the system continues to monitor wheel speeds.
To determine which tyre is deflated the central processing unit 10 calculates for each wheel a deflation indicating factor IMC1-IMC4. These factors are calculated according to the following procedure: IMC1 = Cl if the first deciding factor (MCI) is greater than the central deciding factor (MPSD) then
IMC2 = C2/[ ((C4/C3)/2) + 0.5]
IMC3 = C3/[ ((C4/C2)/2) + 0.5] IMC4 = C4/[ [ ((C4/C3)/2) + 0.5] x [ ((C4/C2)/2) + 0.5]]; if the second deciding factor (MC2) is greater than the central deciding factor (MPSD) then
IMC2 = C2/[ ((C4/C3)/2) + 0.5]
IMC3 = C3/[ ((C3/Cl)/2) + 0.5] IMC4 = C4/[ [ ((C4/C3)/2) + 0.5] x [ ((C3/Cl)/2 + 0.5)]]; if the third deciding factor (MC3) is greater than the central deciding factor (MPSD) then
IMC2 = C2/[ ((C2/Cl)/2) + 0.5]
IMC3 = C3/[ ((C4/C2)/2) + 0.5] IMC4 = C4/[ [ ((C2/Cl)/2) + 0.5] x [ ((C4/C2)/2) + 0.5]]; if the fourth deciding factor (MC4) is greater than the central deciding factor (MPSD) then IMC2 = C2/[ ((C2/Cl)/2) + 0.5] IMC3 = C3/[ ((C3/Cl)/2) + 0.5]
IMC4 = C4/[ [ ((C2/Cl)/2) + 0.5] x [ ((C3/Cl)/2) + 0.5]]; or if none of the deciding factors (MCI, MC2, MC3, MC4) is greater than the central deciding (MPSD) factor then IMC2 = C2/[ (((C2 + C4)/(C1 + C3))/2) + 0.5] IMC3 = C3/[ (((C3 + C4)/(C1 + C2))/2) + 0.5] IMC4 = C4/[ [ (((C3 + C4)/(C1 + C2))/2) + 0.5] x [ (((C2 + C4)/(C1 + C3))/2) + 0.5]]. Thus having obtained a deflation indicating factor for each of the four wheels the central processing unit compares these to determine which wheel has the factor of the largest magnitude. A signal is then sent to operate the indicator light corresponding to that wheel in order to alert the driver that the tyre concerned has deflated. In a preferred arrangement the warning signal is only sent after three sets of deflation indicating factors, calculated from successive sets of wheel speed data, all indicate that a particular tyre is deflated. Whilst the above embodiment has illustrated the method of the invention using the signal data from a multi-toothed wheel system typically producing 48 or 96 pulses per wheel revolution the invention can equally be used with other wheel speed sending systems. For example the method may be used with a simple system which uses a single pulse per revolution to compute the time period for one rotation of each wheel, in which case it will be necessary to multiply the wheel speeds by a constant factor to obtain data in the necessary form. Furthermore whilst the method of the invention has been illustrated by reference to the aforementioned values of constants A and B related to specific vehicles, values of constants A and B in the ranges of -5.0E-7 to +5.0E-7 and -4.0E-9 to +4.0E-9 respectively have been found useful in the invention. Values of A and B in the ranges -2.0E-7 to +2.0E-7 and -2.0E-9 to +1.0E-9 have been found particularly useful in practise of the invention. INDUSTRIAL APPLICABILITY According to a method of the present invention, difference of tyre deflections in each of the tyres due to vehicle characteristics can be accommodated to avoid false signals. Deflation for substantially all the time when the vehicle is running can be detected. The method can be widely applied to vehicles such as cars and trucks.

Claims

1. A method of detecting a deflated tyre on a vehicle by comparing the rolling radii of the tyres by means of comparing angular velocity speed signals from wheel speed sensors one at each wheel characterised by calculating an error value (DEL') where
[ (Cl+C4)/2-(C2+C3)/2] x 100 (Cl + C2 + C3 + C4)/4
where Cl, C2, C3 and C4 are angular velocity values for left-hand front (1), right-hand front (2), left-hand rear (3) and right-hand rear (4) wheels of the vehicle respectively, determining a correction factor (LAT), calculating a corrected error value (DEL) where
DEL = DEL' - DELCOR wherein DELCOR = (LAT x A) + (B x LAT2) wherein A and B are vehicle related constants, and operating a tyre warning indicator (12, 13, 14, 15) provided in the vehicle to indicate that at least one tyre is deflated when it is sensed that the magnitude of the corrected error value DEL is in the range 0.05 to 0.5.
2. A method of detecting a deflated tyre according to claim 1 characterised in that the correction factor LAT is selected by calculating from the four angular velocity values Cl, C2, C3 and C4 respective first, second, third and fourth deciding factors MCI, MC2,
MC3, MC4 where
MCI = Cl
MC2 = C2/[ (C2 + C4)/(C1 + C3)]
MC3 = C3/[ (C3 + C4)/(C1 + C2)] MC4 = C4/[ [ (C2 + C4)/(C1 + C3)] x [ (C3 + C4)/(C1 + C2)]], then summing the four deciding factors and multiplying this sum by a centralising constant K to give a central deciding factor MPSD and selecting the correction factor LAT as follows, if the first or second deciding factor MCI or MC2 is greater than the central deciding factor MPSD then LAT = 2 x (C3 - C4) (Cl + C2 + C3 + C4), if the third or fourth deciding factor MC3 or MC4 is greater than the central deciding factor MPSD then LAT = 2 x (Cl - C2) x (Cl + C2 + C3 + C4), or if none of the deciding factors MCI, MC2, MC3 or MC4 is greater than the central deciding factor MPSD then LAT = (Cl + C3 - C2 - C4) * (Cl + C2 + C3 + C4).
3. A method of detecting a deflated tyre according to claim 2 characterised in that the centralising constant K has a value in the range 0.250125 to 0.250625.
4. A method of detecting a deflated tyre according to claim 2 characterised in that the centralising constant K has a value of 0.25025.
5. A method of detecting a deflated tyre according to claim 2, 3 or 4 characterised in that a deflation indicating factor IMC1, IMC2, IMC3, IMC4 is calculated for each wheel (1, 2, 3, 4) respectively and the wheel (1, 2, 3, 4) having the numerically greater deflation indicating factor is indicated as deflated, where the deflation indicating factors are calculated as folows:
IMC1 = Cl, then if the first deciding factor MCI is greater than the central deciding factor MPSD then
IMC2 = C2/[ ((C4/C3)/2) + 0.5]
IMC3 = C3/[ ((C4/C2)/2) + 0.5]
IMC4 = C4/[[ ((C4/C3)/2) + 0.5] x [ ((C4/C2)/2) + 0.5]]; if the second deciding factor MC2 is greater than the central deciding factor MPSD then
IMC2 = C2/[ ((C4/C3)/2) + 0.5]
IMC3 = C3/[ ((C3/Cl)/2) + 0.5] IMC4 = C4/[ [ ((C4/C3)/2) + 0.5] x [ ((C3/Cl)/2) + 0.5]]; if the third deciding factor MC3 is greater than the central deciding factor MPSD then
IMC2 = C2/[ ((C2/Cl)/2) + 0.5]
IMC3 = C3/[ ((C4/C2)/2) + 0.5]
IMC4 = C4/[ [ ((C2/Cl)/2) + 0.5] [ ((C4/C2)/2) + 0.5]]; if the fourth deciding factor MC4 is greater than the central deciding factor MPSD then IMC2 = C2/[ ((C2/Cl)/2) + 0.5]
IMC3 = C3/[ ((C3/Cl)/2) + 0.5]
IMC4 = C4/[ [ ((C2/Cl)/2) + 0.5] x [ ((C3/Cl)/2) + 0.5]]; or if none of the deciding factors MCI, MC2, MC3, MC4 is greater than the central deciding MPSD factor then IMC2 = C2/[ (((C2 + C4)/(C1 + C3))/2) + 0.5]
IMC3 = C3/[ (((C3 + C4)/(C1 + C2))/2) + 0.5]
IMC4 = C4/[ [ (((C3 + C4)/(C1 + C2))/2) + 0.5] x [ (((C2 + C4)/(C1 + C3))/2) + 0.5]].
6. A method of detecting a deflated tyre according to any of claims 1 to 5 characterised in that the tyre warning indicator (12, 13, 14, 15) is operated when it is sensed that the magnitude of the corrected error value DEL is in the range 0.1 to 0.3.
7. A method of detecting a deflated tyre according to any of claims 1 to 6 characterised in that the value of the vehicle related constant A is in the range -5.0E-7 to +5.0E-7 and the values of vehicle related constant B is in the range -4.0E-9 to +4.0E-9.
8. A method of detecting a deflated tyre according to any one of claims 1 to 6 characterised in that the value of the vehicle related constant A is in the range -2.0E-7 to +2.0E-7 and the value of the vehicle related constant B is in the range -2.0E-9 to +1.0E-9.
9. A method of detecting a deflated tyre according to any of claims 1 to 6 characterised in that the value of the vehicle related constants A and B are -1.8E-7 and -6.2E-10 respectively.
10. A method of detecting a deflated tyre according to any of claims 1 to 6 characterised in that the value of the vehicle related constants A and B are +1.0E-7 and +4.6E-10 respectively.
11. A method of detecting a deflated tyre according to any of claims 1 to 6 characterised in that the value of the vehicle related constants A and B are -3.3E-8 and -1.8E-10 respectively.
12. A method of detecting a deflated tyre on a vehicle according to any of claims 1 to 6 characterised in that the value of the vehicle related constants A and B are +1.4E-7 and -1.4E-9 respectively.
EP94910552A 1993-04-01 1994-03-29 Method of detecting a deflated tyre on a vehicle Expired - Lifetime EP0642427B1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
GB939306846A GB9306846D0 (en) 1993-04-01 1993-04-01 Method of detecting a defalted tyre on a vehicle
GB9306846 1993-04-01
PCT/JP1994/000501 WO1994022681A1 (en) 1993-04-01 1994-03-29 Method of detecting a deflated tyre on a vehicle

Publications (2)

Publication Number Publication Date
EP0642427A1 true EP0642427A1 (en) 1995-03-15
EP0642427B1 EP0642427B1 (en) 1997-03-05

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EP (1) EP0642427B1 (en)
JP (1) JP2735387B2 (en)
KR (1) KR100307088B1 (en)
AT (1) ATE149433T1 (en)
AU (1) AU670683B2 (en)
CA (1) CA2136072C (en)
DE (1) DE69401879T2 (en)
ES (1) ES2098128T3 (en)
GB (1) GB9306846D0 (en)
WO (1) WO1994022681A1 (en)

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US5838230A (en) * 1992-07-11 1998-11-17 Sumitomo Rubber Industries, Ltd. Method of detecting a deflated tire on a vehicle
JP3509331B2 (en) * 1995-10-11 2004-03-22 本田技研工業株式会社 Vehicle wheel pressure reduction judgment device
US5721374A (en) * 1996-08-19 1998-02-24 Delco Electronics Corporation Method of detecting low tire pressure by comparing wheel speeds
US5760682A (en) * 1997-03-07 1998-06-02 Robert Bosch Gmbh Method for detecting a deflated tire on a vehicle
DE69930060T2 (en) * 1998-04-02 2006-09-21 Sumitomo Rubber Industries Ltd., Kobe Device and method for warning against tire pressure loss
US6222444B1 (en) 2000-04-03 2001-04-24 Robert Bosch Corporation Method for detecting a deflated tire on a vehicle
US6285280B1 (en) 2000-06-26 2001-09-04 Robert Bosch Corporation Method for detecting a deflated tire on a vehicle
US6459369B1 (en) 2000-11-22 2002-10-01 Robert Bosch Corporation Tire deflation detection system with feedback component
US6774776B2 (en) 2002-07-30 2004-08-10 Sumitomo Rubber Industries, Ltd. Method and apparatus for alarming decrease in tire air-pressure
KR101647696B1 (en) * 2015-07-13 2016-08-11 현대오트론 주식회사 Apparatus and method for monitoring tire pressure using radius analysis

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AU670683B2 (en) 1996-07-25
KR100307088B1 (en) 2002-04-24
GB9306846D0 (en) 1993-05-26
CA2136072A1 (en) 1994-10-13
AU6291594A (en) 1994-10-24
CA2136072C (en) 2002-05-28
US5589816A (en) 1996-12-31
ES2098128T3 (en) 1997-04-16
DE69401879T2 (en) 1997-06-12
EP0642427B1 (en) 1997-03-05
WO1994022681A1 (en) 1994-10-13
ATE149433T1 (en) 1997-03-15
JP2735387B2 (en) 1998-04-02
JPH08501040A (en) 1996-02-06
KR950701867A (en) 1995-05-17
DE69401879D1 (en) 1997-04-10

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